Membrane wiring boards are used as inter-board connection wiring materials of laptop computers and switching circuits for digital home appliances. Membrane wiring boards are obtained by printing silver paste onto a flexible film substrate made of plastic and the like to form a circuit layer (see Patent Document 1). Consequently, membrane wiring boards can be manufactured more easily and less expensively than flexible printed circuit (FPC) boards comprising a circuit layer formed by etching or plating copper on a plastic film. Thus, membrane wiring boards are coming to be used as inexpensive alternatives to FPC.